AUTHOR=Zhou Ting , Hua Yingpeng , Huang Yupu , Ding Guangda , Shi Lei , Xu Fangsen 

TITLE=Physiological and Transcriptional Analyses Reveal Differential Phytohormone Responses to Boron Deficiency in Brassica napus Genotypes

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00221

DOI=10.3389/fpls.2016.00221

ISSN=1664-462X

ABSTRACT=<p>Phytohormones play pivotal roles in the response of plants to various biotic and abiotic stresses. Boron (B) is an essential microelement for plants, and <italic>Brassica napus</italic> (<italic>B. napus</italic>) is hypersensitive to B deficiency. However, how auxin responds to B deficiency remained a dilemma for many years and little is known about how other phytohormones respond to B deficiency. The identification of B-efficient/inefficient <italic>B. napus</italic> indicates that breeding might overcome these constraints in the agriculture production. Here, we seek to identify phytohormone-related processes underlying B-deficiency tolerance in <italic>B. napus</italic> at the physiological and gene expression levels. Our study indicated low-B reduced indole-3-acetic acid (IAA) concentration in both the shoots and roots of <italic>B. napus</italic>, and affected the expression of the auxin biosynthesis gene <italic>BnNIT1</italic> and the efflux gene <italic>BnPIN1</italic> in a time-dependent manner. Low-B increased the jasmonates (JAs) and abscisic acid (ABA) concentrations and induced the expression of the ABA biosynthesis gene <italic>BnNCED3</italic> and the ABA sensor gene <italic>BnPYL4</italic> in the shoot. In two contrasting genotypes, the auxin concentration decreased more drastically in the B-inefficient genotype ‘W10,’ and together the expression of <italic>BnNIT1</italic> and <italic>BnPIN1</italic> also decreased more significantly in ‘W10’ under long-term B deficiency. While the JAs concentration was considerably higher in this genotype, and the ABA concentration was induced in ‘W10’ compared with the B-efficient genotype ‘QY10.’ Digital gene expression (DGE) profiling confirmed the differential expression of the phytohormone-related genes, indicating more other phyohormone differences involving in gene regulation between ‘QY10’ and ‘W10’ under low-B stress. Additionally, the activity of DR5:GFP was reduced in the root under low-B in <italic>Arabidopsis</italic>, and the application of exogenous IAA could partly restore the B-defective phenotype in ‘W10.’ Overall, our data suggested that low-B disturbed phytohormone homeostasis in <italic>B. napus</italic>, which originated from the change of transcriptional regulation of phytohormones-related genes, and the differences between genotypes may partly account for their difference in tolerance (B-efficiency) to low-B.</p>